Circuits for space-current devices



June 5', 1928. 1,672,733

A. RIVET CIRCUITS FOR SPACE CURRENT DEVICES Filed July 5, 1924 Im/ernor' flneir'efeuef. DEC'D. Henri/Qt 2/85,-

' Le a! fi yvresenazr'ra y His Attorney Patented June 5, 1928.

UNITED STATES 1,672,733 PATENT OFFICE.

ANDRE RIVET, DECEASED, LATE OF PAR-IS, FRANCE, BY HENRI RIVE'I, LEGAL REPRE- SEN'IA'IIVE, OF PARIS, FRANCE; SAID HENRI RIVET, HEIR, .ASSIGNOR '10 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

CIRCUITS FOR SPACE-CURRENT DEVICES.

Application filed July 3, 1924, Serial No. "724,146, and in France July 5, 1923.

This invention relates to improvements in circuits for space current devices.

The purpose of the invention is to provide a circuit in which three electrode space current devices may be operated by alternating current.

It is well known that when direct current is used for operating a three electrode space current device having interconnecting apparatus associated in circuit relation therewith the result is that the difference in potential between the extreme ends of the filament is equal to the voltage impressed upon said filament. When direct current is used thedifference in potential does not interfere wit-h the efficiency of the device, but in the case of alternating current the variations in potential difierence between the grid and filament and particularly the variations in the plate current interfere with reception and hence are objectionable. It is one of the objects of the invention to arrange the circuit of the space current device in such manner that such current variations areobviated or at leastreduced to a minimum when alternating current is used'for hat'ingthe filament. 7

A further object of the. invention is to devise a circuit in which ordinary industrial alternating current sources may be used without the danger of introducing into the circuitdisturbances such as the well-known alternating current hum.

The theory of the invention and its application to the circuits of space current devices will be readily understood byreference to the. following specification taken in con-v junction with the accompanying drawing while the scope of the invention will be set forth in the appended claims.

Referring to the drawings, Figure 1 illustrates a conventional detector circuit adapted for alternating current operation. Figure 2 designates a single stage amplifier also adapted for alternating current operation and in which the grid and plate are connected directly to points on the filament.

In considering the ordinary single stage amplifier circuit comprising an input circuit, an output circuit and sources of direct cur-. .rent for operating the filament, plate and grid it is assumed that suitable excitation and outputtransformers are associated with the three electrode space current device and that the most satisfactory region of the character- .istic in which said space current device operates is governed by the grid voltage supplied by a direct current source.

In operating such an amplifier circuit with alternating current, as indicated in Figure 2 assume that the grid and plate are connected directly to points located between A and B on the filament and that the center 0 of said filament is'taken as the zero of the potentials, N representing the point of attachment of the grid and M that of the plate. The filament A B is heated by an alternating current source having a voltage represented by U=Um Sin' wt Um being the maximum pressure. By connecting a potentiometer A B to the-terminals of the filament, either the grid or the plate may be connected to an equipo- 'tential point of any part of the filament.

If, now, the grid be connected to any point N on the filament or of its equivalent on the potentiometer N, and if the plate be connected to any other point M or M, a variable plate current will be set up in addition to the direct current.

If the points M and N are properly located on the potentiometer, the plate current will be quite -constant. Equilibrium conditions may be attained by arbitrarily selecting the position of either point, say M, and then manipulating the position of its counterpart N upon the potentiometer until optimum circuit conditions are secured.

If the plate is connected to any point M then the location of the point N on the filament may be determined by the follow-' ing calculation: let 1 be the distance ON,

A the distance OM and2L the length of the filament which is assumed to be homogeneous.

At any moment t, the voltage at the terj minals of the filament AB isUm Sin t; the alternating grid voltage isl/2' of Um Sin wt A Sill wt L and that or the plate 1 2 Um (wt) the alternating plate current. Then b represents the displacement of the plate in which Im will be zero whatever ma current with respect to the voltage U.

The following relation will then exist between the alternating plate current and the variations in gridand plate voltage %U=m Sin wt (M be the value of t if the second member 0 the equation is zero, that is to say if inasmuch as K is assumed to be positive and greater than unity.

- The two special cases which occur most frequently in actual practice are 1. .\==L where 1= K nected to one of the ends of the filament.

2. )\=0 where 1=O the points of attachment of the grid and plate being connected to ether at point 0.

'al that the plate be conthe plate being cont is not essent1 nected to the exact middle point of the filament or even to an equ1 otential oint. This point may be any one, ut once c osen the position of the point of attachment of the grid is overned by this choice. Upon the ro er etermination of this point depends t e successful alternating current operation of a three electrode space current device.

Figure 1 shows an arrangement of a detector circuit ada ted for alternating current operation. T he voltage of the source P must be chosen so that the grid potential causes the valve to operate on an elbow or kink of the plate characteristic which is, however, sufiicientl large to permit slight variation of the of the space current device. Y

Alternating current may also be used for operating a plurality of three electrode space current devices connected in cascade in accordance with the principles set forth above for single stage work. It is to be ranging and adjusting the connecting apparatus, transformer, or the like between two consecutive three electrode space current devices in an amplifying circuit operating at say a frequency F that its output is the maximum at that frequency. When alternating curernt is used for heating the filament the connecting apparatus must then be so arranged and adjusted that the output is very smal with respect to the frequency of the feedin current and its harmonics, particularly t e second harmonic, as compared with the output at the frequency to be amplified. Under these conditions any noise caused by the heating current of a given space current device is transmitted but slightly or else not at all to the next succeeding device thus permitting quiet amplication. y

In the case of hi h frequency amplication the above describe results may readily be obtained-but strict adherence to these conditions is especially necessary in connection with audio frequency amplification. In this case the circuits must be designed to lower the output of the apparatus when commercial frequencies are used without appreciably decreasin their audio fre ueney output. This may e accomplished or example by placing an air gap 1n the magnetic circuit of the connecting transformer, inserting resonant shunt circuits or inserting one or more artificial lines between the space .current devices or after the last amplifier.

In the preferred form of the invention the grid and the plate are connected to suitable points of a potentiometer connected to the terminals of the filament, but the arrangement is not limited to the use of a potentiometer and may be varied without departing from the scope of the invention for example by connecting the grid and the plate to suitable points of the winding of the supply transformers.

What is claimed as new and desired to be secured by Letters Patent of the United States 1. The combination with an electrical discharge device having a cathode adapted to be heated, a cooperating anode and a discharge controlling grid, of a source of alternating current applied to said cathode for heating purposes, external circuit connections between said cathode and anode and between said cathode and grid, and means for independently adjusting the connections of the anode and grid to the cathode in such a Way that variations in anode potential due to the heating current of the cathode may be compensated for by variations in the grid potential produced by the source ofv heating current.

2. The combination with an electrical discharge device having a cathode adapted to be heated, a cooperating anode and a discharge controlling grid, of a source of alternating current applied to said cathode for heating purposes, a potentiometer in shunt with said cathode, external circuit connections between said cathode and anode and between said cathode and grid, and means for independently adjusting the connections of the anode and grid to the cathode through said potentiometer 'to compensate for the variations in anode potential caused by the heating current of the cathode.

3. The method of eliminating the alternating current hum from the output circuit of a space discharge device provided with a cathode connected to alternating current terminals in shunt to a potentiometer and with a grid and anode connected to said potentionieter through different terminals, which comprises adjusting one of said terminals, and independently adjusting the other of said terminals.

In witness where0f,'I have hereunto set my hand this 23d day of June, 1924.

HENRI RIVET, 

